What is it?

Ash dieback is a disease of Ash trees (Fraxinus Excelsior) caused by the fungus Chalara Fraxinea. The disease causes leaf loss and crown dieback in affected trees and leads to the hosting trees death.

Ash is a very important tree in the UK both ecologically and culturally so this disease is causing great concern about the damage it will do.

The proportion of trees with a high level of natural resistance seem to be very low, probably less than 5%.

Trees show a 10 – 15% decline in the canopy in a single year and anecdotal reports from areas of the UK currently infected by ash dieback support this as a typical rate of decline. However, some individual trees (depending on their health and condition) could decline much more rapidly.

How does it affect the tree?

The disease is spread by spores from the fruiting bodies of the fungus produced on fallen ash leaves. These airborne spores can disperse naturally via wind over tens of kilometres. It can also occur at the base of trunks (the root collar) and through root infection.

Evidence suggests young trees are killed quickly while many mature ash trees can resist infection for some time until eventually dying or becoming weakened and succumbing to attack from another pest or pathogen.

Root-attacking fungi such as honey fungus can hasten the death of woodland trees affected by ash dieback causing the tree to become unstable, shed branches and eventually succumb to the disease.

Symptoms

Dark lesions – often long, thin and diamond-shaped – appear on the trunk at the base of dead side shoots

– The tips of shoots become black and shrivelled

– Blackened, dead leaves – may look a bit like frost damage

– The veins and stalks of leaves, normally pale in colour, turn brown

– Saplings have dead tops and side shoots

– In mature trees, dieback of twigs and branches in the crown, often with bushy growth further down the branches where new shoots have been produced

– In late summer and early autumn (July to October), small white fruiting bodies can be found on blackened leaf stalks

Action

The aim of management, should be to slow the spread, minimise the impact of the disease, and preserve as many Chalara – tolerant ash trees as possible.

We should avoid felling Ash trees that show no sign of the infection as there is a small percentage of trees showing resilience and surviving. These trees might be the key to combating the disease so we should try to retain them.

Trees in areas with high levels of public access therefore need to be monitored carefully for risks to public safety, and some felling or pruning of dead or dying trees is advisable if risk assessments show they are a hazard. When assessing trees’ health, look for signs of lesions (cankers) or honey fungus (Armillaria) near the base of the trunks: these can weaken the trunks and make the trees more prone to falling.

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The task included clearing large areas of trees and shrubs under ecological supervision. There was an old wall running (200m) along one of the site boundaries which needed to be cleared of bramble to allow access for surveying. Along the old slip ways there had been earth piled up against the walls which also had to be removed for surveying.

Vegetation clearance lasted 6 weeks.

Many of the trees and shrubs were felled and cleared by hand and processed by our tracked woodchipper. Some areas of the site were of marshland and riverbank and recorded as Sites of Special Scientific Interest. With the fast-rising tides, we decided it would be quicker and safer to use an excavator with tree shears to remove the trees from the awkward locations. All vegetation had to be cut down to 500mm to then be dug out after ecological inspection. We used excavator and flail for areas of dense shrubbery and small trees.

The old retaining wall along the site boundary had become overgrown with Budlear, Ivy and other weeds, therefore the integrity of the wall could not be determined prior to clearance. Using a tracked MEWP and long reach hedge trimmers we worked along the wall removing the vegetation to reveal the walls condition underneath.

The slip ways where the ships once sat had debris piled up against their retaining walls, therefore removal of this spoil was also required to assess the condition of these retaining walls. During excavation asbestos was identified, therefore a specialist was informed and removed the asbestos from site.

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Prior to the proposed housing development at Ty Fry Farm in Lougher areas of the site had to be cleared of vegetation. Further to this the remaining trees needed tree protective fencing installed and the site secured with Heras fencing. 

Consisting of several old farm fields the majority of the vegetation was along the edges. The trees were a wide variety of native species. Key species such as Oak, Ash and Birch were retained as these would add value to the environment. Operating closely to the arboricultural survey provided clearance and arboricultural pruning works were carried out. 

First stage of the process was to remove trees and vegetation that that was not to be retained. Less favoured species such as Willow, Alder and Poplar were targeted for removal. All the large trees were climbed if necessary, felled and processed. Large areas of dense Blackthorn and Hawthorn were flailed using an Excavator. Using the 18-tonne excavator with flail attachment made easy work of this, flailing upto 8/9 inch thick. 

Second Stage  

Using an Excavator all the stumps were dug out and then removed from site. The site was a bog so the only way to extract the stumps were to load them out on the back of a tractor. Even that struggled at times so had to be pushed out by the excavator. 

In preparation for the development the remaining trees were to be pruned to facilitate potential buildings and roads. A variety of pruning works were carried out by our team of climbers, crown lifting and reducing where necessary, all works carried out to BS3998. Once this was completed the Veg Clearance phase was completed. 

After Clearance it was required that 1.5km of Tree Protective Fencing was installed to protect the trees remaining for the duration of the project. To complete the project for us we filled all gaps with Heras fencing leaving the site ready for work to commence. 

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In preparation for the redevelopment of St Cyres School in Dynas Powys areas of vegetation at the site had to be cleared in order for construction to take place. Further to ecological surveying the site was found to have Dormouse habitat present along with potential bat roosting. 

Summer clearance began in September through to October. During this phase areas were cleared in small quantities (50m2) under ecologists supervision. Thus, allowing any potential wildlife (nesting bids, dormice, bats etc) to have time to vacate the areas to vegetation remaining. We then moved between different areas of the site not returning to any area cleared for less than 24 hours. All vegetation was cut down to 500mm ecologists then supervised the stump removal to ensure no wildlife was present. The only machines used during this clearance were woodchippers to process the timber and an excavator to dig the stumps out. Any machine power would have been too destructive to the sensitive habitat. So, using chainsaws and brush cutters vegetation was cleared to give wildlife the safest opportunity to vacate. 

Some trees were flagged after inspection to have bats potentially roosting. Following a thorough inspection by our climbers with an endiscope the trees were section felled. No bats were found. 

Phase 2 – Winter Clearance 

Starting in January running through to February extensive clearance was carried out at site. Dense areas of Hawthorn, Blackthorn amongst various other species had been flagged as potential dormouse habitat. 

Under ecologists supervision all scrub and trees cleared were cut down to 500mm. Further to ecologists inspection to ensure no nesting dormice were present the stumps were removed. Due to the ecological requirements machines were not allowed to be used at site for clearance because of the potential damage to the habitat. So everything was cut by hand removed by hand from the area being cleared and chipped outside to avoid tracking machines in the sensitive environment. 

A scheme to replant the vegetation cleared here is in progress to mitigate the habitat lost by the initial clearance phases. A mix of translocating and new planting should provide a sustainable environment for the future.  

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The trees were in two sections. A number stood in an area that we could drop sections into, other than railside where everything was lowered and brought round. The others had to be completely rigged as there was no drop zone.

Felling large sections out into the open drop zone proved to be effective making good progress. When rigging due to the brittle nature of the tree’s we avoided rigging off the stems with the climber in. Using various rigging techniques and lowering equipment meant we could bring down sections in sufficient sizes without posing risk to the climbers. Accurate cutting by the climbers meant sections landed just where we wanted them making the ground teams job safer and quicker. Trees were felled laying stems next to each other to be cut into sections and removed by an excavator and lorry.

The second section proved to be a little more difficult as the working area became smaller. Using Span rigging meant that we could maximise the size of the sections that could be lowered whilst working in a confined area. There was also concern for the integrity of some of the trees as ones we had already felled had large cavities of rot and decay. Span rigging holds the sections weight off two separate trees, allowing the climber to cut without the load on the tree they’re anchored to, making it far safer and quicker as rigging points are fixed. Also saves the potential cost of crane hire.

With only a couple of feet of soft ground around the trunk of each tree the only option was to soft fell each stem, lowering it slowly to ground whilst tip tied to a rigging point.

After removing the trees, it was requested that the stumps be ground out and a new line of Limes (Tilia) were planted to replace the removed Lombardy’s.

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